Method of manufacturing thin film transistor

ABSTRACT

The object of the present invention is to form a low-concentration impurity region with good accuracy in a top gate type TFT. Phosphorus is added to a semiconductor layer by using a pattern made of a conductive film as a mask to form an N-type impurity region in a self-alignment manner. A positive photoresist is applied to a substrate so as to cover the pattern and then is exposed to light applied to the back of the substrate and then is developed, whereby a photoresist  110  is formed. The pattern is etched by using the photoresist pattern as an etching mask to forma gate electrode. A channel forming region, a source region, a drain region, and low-concentration impurity regions, are formed in the semiconductor layer in a self-alignment manner by using the gate electrode as a doping mask.

BACKGROUND OF THE INVENTION

This application is a continuation of copending U.S. application Ser.No. 13/567,196 filed on Aug. 6, 2012 which is a continuation of U.S.application Ser. No. 13/242,715 filed on Sep. 23, 2011 (now U.S. Pat.No. 8,237,169 issued Aug. 7, 2012) which is a continuation of U.S.application Ser. No. 12/240,367 filed on Sep. 29, 2008 (now U.S. Pat.No. 8,030,658 issued on Oct. 4, 2011) which is a continuation of U.S.application Ser. No. 11/890,340 filed on Aug. 6, 2007 (now U.S. Pat. No.7,446,340 issued Nov. 4, 2008) which is a continuation of U.S.application Ser. No. 11/051,005 filed on Feb. 4, 2005 (now U.S. Pat. No.7,253,441 issued Aug. 7, 2007) which is a continuation of U.S.application Ser. No. 09/916,913, filed on Jul. 27, 2001 (now U.S. Pat.No. 6,853,004 issued Feb. 8, 2005) which is a continuation of U.S.application Ser. No. 09/449,140, filed on Nov. 24, 1999 (now U.S. Pat.No. 6,277,679 issued Aug. 21, 2001).

1. Field of the Invention

The present invention relates to a method of manufacturing a thin filmtransistor and an active matrix substrate using the thin film transistoras a switching element.

2. Description of the Related Arts

A thin film transistor (hereinafter referred to as a TFT) is utilizedfor the switching element of a pixel electrode of an active matrix typeliquid crystal display device. As the demand for a high-definitionliquid crystal display grows, the semiconductor layer of the TFT isrequired to be formed of polycrystalline silicon instead of amorphoussilicon.

If the semiconductor layer of a TFT is formed of polycrystallinesilicon, it is possible to manufacture the TFT such that it has highmobility and a large on-current, and hence not only a pixel matrixcircuit but also a driver circuit can be integrally formed on the samesubstrate. However, in the TFT using the polycrystalline silicon, acurrent leaking from a drain in an off state (that is, off current) islarge, and hence, if it is used as the switching element of a matrixcircuit, it can not hold the electric potential of the pixel electrode.Therefore, it has been a big problem to reduce the off current of theTFT.

In order to solve this problem, an attempt has been made to relievevoltage concentrated on the drain and to reduce the off current bymaking a TFT having an offset structure or a light doped drain structure(hereinafter referred to as an LDD structure). A method of manufacturingthe TFT having the LDD structure will briefly be described by the use ofFIG. 9.

An underlayer film 11 made of a silicon oxide film is formed on a glasssubstrate 10. An amorphous silicon film is formed on the underlayer film11 and is polycrystallized by applying an excimer laser thereto. Thepolycrystallized silicon film is patterned in a shape of island to forma semiconductor layer 12. A gate insulating film 13 made of siliconoxide is formed such that it covers the semiconductor layer 12. A metalfilm made of aluminum, tantalum, or the like is formed on the gateinsulating film 13. A photoresist mask 14 is formed and the metal filmis patterned in a predetermined shape by using the photoresist mask 14to form a gate electrode 15 (see FIG. 9 (A)).

The photoresist mask 14 is removed and then impurities to be donors oracceptors are added to the semiconductor layer 12 by ion doping or byion implantation by using the gate electrode 15 as a doping mask,whereby impurity regions 16, 17 are formed in the semiconductor layer 12in a self-alignment manner (see FIG. 9(B)).

A photoresist mask 18 is formed which is wider in the direction oflength of channel than the gate electrode 15. The length of alow-concentration impurity region is determined by the shape of thephotoresist pattern 18 (see FIG. (C)).

Impurities to be donors or acceptors are added to the semiconductorlayer 12 by ion doping or by ion implantation by using the photoresistpattern 18 as a doping mask, whereby a source region 21, a drain region22, and low-concentration impurity regions 24, 25 are formed in thesemiconductor layer 12 (see FIG. 9(D)).

The photoresist pattern 18 is removed and then the impurities added tothe semiconductor layer 12 are activated by applying laser light to thesubstrate or by heating the substrate. An interlayer insulating film 27comprising silicon oxide film is formed. Contact holes, that lead to thesource region 21, the drain region 22, or the terminal part (not shown)of the gate electrode 15, are made in the interlayer insulating film 27.A metal film made of titanium or the like is formed and is patterned toforma source electrode 28, a drain electrode 29 and the lead wiring (notshown) of the gate electrode 15 (see FIG. 9(E)).

In a conventional manufacturing method shown in FIG. 9, the photoresistpattern 18 is used as a doping mask so as to make an LDD structure.Therefore, in order to form the low-concentration impurity region withhigh accuracy, a photolithography mask is required to be aligned withhigh accuracy, but there is a problem that as an element becomes finerand a liquid crystal panel becomes larger in area, an alignment accuracybecomes lower.

Therefore, in order to solve the above problem, the present applicantdiscloses a technology for manufacturing a TFT having an LDD structurein a self-alignment manner in Japanese Patent No. 2759415. In the aboveJapanese Patent, aluminum is used as a gate electrode material and theLDD structure is formed in a self-alignment manner by using an anodicoxide (alumina) by an oxalic acid and an anodic oxide (alumina) by atartaric acid as the doping masks.

In the above Japanese Patent, a photoresist is not used as the dopingmask and hence the length of the low-concentration impurities region canbe controlled with high accuracy, but there is a drawback that the gateelectrode material is limited to aluminum. Also, there is anotherproblem that the process temperature is limited to about 400° C. afteran aluminum wiring is formed and that aluminum atoms are diffused into agate insulating film to easily make a short circuit between a gatewiring and a channel, thereby reducing reliability.

Further, in an anodic oxidation process, each gate electrode/wiringmakes a short circuit with a voltage supply line, but after an anodicoxidation, it is necessary to etch away the voltage supply and theconnection potion of the voltage supply line and the gate wiring and toelectrically separate all the gate wirings/electrodes. Therefore, it isnecessary to arrange a circuit in consideration of the process margin ofetching, which prevents a high-integration design.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofmanufacturing a coplanar type (top gate type) TFT having an LDDstructure or an offset structure with high accuracy. It is anotherobject of the present invention to provide a method of manufacturing athin film transistor whose gate wiring (gate electrode) is not limitedto aluminum.

In order to achieve the above objects, according to the presentinvention, a low-concentration impurity region to which donors oracceptors are added is formed in a semiconductor layer in aself-alignment manner by using a gate electrode as a mask. To that end,a conductive film is patterned in two steps to form a gate electrode. Inthis regard, the gate electrode means a part crossing the semiconductorlayer via a gate insulating film in a gate wiring.

First, the conductive film is patterned to form a pattern wider than thelength of a channel. Impurities to be donors or acceptors are added tothe semiconductor layer by using the pattern made of the conductivefilm. The pattern made of the conductive film is patterned and madeslender in the direction of length of the channel to form the gateelectrode.

The patterning mask of this patterning process is formed by exposing apositive photoresist to the light applied to the back of a transparentsubstrate and by developing it. The pattern made of the conductive filmfunctions as a photolithography mask when the transparent substrate isexposed to the light applied to the back thereof and a photoresistpattern can be formed on the pattern made of the conductive film in aself-alignment manner. The photoresist pattern narrower than the patternmade of the conductive film can be formed with good accuracy bycontrolling an exposure time and a developing time.

In this connection, in the present specification, the surface of thesubstrate means a surface on which the semiconductor layer is formed andthe back of the substrate means a face opposite thereto.

The low-concentration impurity region is formed in a self-alignmentmanner by adding impurities by using the gate electrode which isnarrower than the pattern made of the conductive film as the mask.

According to the present invention, the length of the low-concentrationimpurity region is determined by the photoresist pattern like theconventional method, but the photoresist pattern in accordance with thepresent invention is formed in a self-alignment manner by exposing thesubstrate to the light applied to the back thereof and the width of thephotoresist pattern can be formed with high accuracy by controlling theexposing time and the developing time. Therefore, even if a thin filmtransistor is made finer and a substrate is increased in area, thelength of the low-concentration impurity region can be controlled withhigh accuracy and with good reproducibility. Further, since the numberof photolithography masks can be omitted by one, costs can be reducedand the number of mask alignment processes is reduced and throughput canbe expected to improve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A)-1(D) are cross-sectional views showing a manufacturingprocess of a TFT in accordance with the present invention. (PreferredEmbodiment 1)

FIGS. 2(A)-2(E) are cross-sectional views showing a manufacturingprocess of a TFT in accordance with the present invention. (PreferredEmbodiment 1)

FIGS. 3(A)-3(E) are cross-sectional views showing a manufacturingprocess of a CMOS circuit in accordance with the present invention.(Example 1)

FIGS. 4(A)-4(E) are cross-sectional views showing a manufacturingprocess of a CMOS circuit in accordance with the present invention.(Example 1)

FIG. 5 is a schematic perspective view of an active matrix type liquidcrystal panel in accordance with the present invention. (Example 2)

FIGS. 6(A) and 6(B) are top plan views of a CMOS circuit, a pixel matrixcircuit in FIG. 5. (Example 2)

FIG. 7 is a cross-sectional view of an active matrix substrate in FIG.5. (Example 2)

FIGS. 8(A)-8(F) are schematic constitutions of electronic devicesmounted with a liquid crystal display device in accordance with thepresent invention. (Example 3)

FIGS. 9(A)-9(E) are cross-sectional views showing a manufacturingprocess of a TFT having a conventional LDD structure.

FIG. 10(A) is an EL panel circuit diagram.

FIG. 10(B) shows a top view of an EL panel pixel.

FIG. 11 is a cross sectional view at III-III′ of FIG. 10(B) showing across section of the switching TFT, storage capacitance, current controlTFT and organic EL element portion.

FIG. 12(A) is a top view of an EL panel which shows pixel area, drivingarea formed on a substrate and FPC which connects the driving area andexternal equipment.

FIG. 12(B) is a cross sectional view at IV-IV′ of FIG. 12(A) showing thestructure of an EL display device.

FIG. 13(A) is a top view of an EL panel which shows pixel area, drivingarea formed on a substrate and FPC which connects the driving area andexternal equipment.

FIG. 13(B) is a cross sectional view at V-V′ of FIG. 13(A) showing thestructure of an EL display device.

FIG. 14 is a cross sectional view of a pixel area.

FIG. 15A is a top view of a pixel area.

FIG. 15B is an example of a circuit diagram of the pixel area of FIG.15A.

FIG. 16 is a cross sectional view showing the structure of an ELelement.

FIG. 17A is an example of a circuit drawing of the pixel area of FIG.15A.

FIG. 17B is an example of a circuit drawing of the pixel area of FIG.15A.

FIG. 17C is an example of a circuit drawing of the pixel area of FIG.15A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments in accordance with the present invention willbe described by using FIG. 1 and FIG. 2.

Preferred Embodiment 1

The present preferred embodiment relates to a manufacturing method of aTFT having an LDD structure. FIG. 1 and FIG. 2 are cross-sectional viewsshowing a manufacturing process and cross-sectional views in thedirection of length of the channel of the TFT.

First, an underlayer film 101 is formed on the whole surface of asubstrate 100, and an island-shaped semiconductor layer 103 is formed onthe underlayer film 101. An insulating film 104 to be a gate insulatingfilm and covering the semiconductor layer 103 is formed on the wholesurface of the substrate 100 (see FIG. 1(A)).

A transparent substrate having a transmissivity of 80% or more, morepreferably, of 90% or more, to light applied to the back of thesubstrate (coherent light having a wavelength 400 nm or less), which isdescribed below, is used as the substrate 100. For example, a glasssubstrate, a quartz substrate, a crystalline glass substrate, and aresin substrate such as a polyethylene terephthalate (PET) or the likecan be used.

The underlayer film 101 is used for preventing impurities such as sodiumions or the like from diffusing from the substrate 100 into thesemiconductor layer 103 and for increasing the adhesive performance of afilm formed on the substrate 100. A single layer or a multi-layer of aninorganic insulating film such as a silicon oxide film, a siliconnitride film, a silicon oxy-nitride film or the like can be used as theunderlayer film 101.

For example, the underlayer film 101 can be formed not only by CVD or bysputtering, but also, in the case of using a heat-resistant substratesuch as a quartz substrate, by forming an amorphous silicon film and bythermally oxidizing the amorphous silicon film, to form a silicon oxidefilm.

It is recommended that the material of the semiconductor layer 103 beselected in accordance with a characteristic required of the TFT, andthe following materials can be used as the semiconductor layer 103:amorphous silicon, amorphous silicon germanium, or amorphous germanium,or crystalline silicon, crystalline germanium, or crystalline silicongermanium, each of which is made by crystallizing each of theseamorphous semiconductor films by applying a laser to it or by subjectingit to heating treatment. The thickness of the semiconductor layer 103 ismade 10 nm to 150 nm.

The underlayer film 101 is used for preventing impurities such as sodiumions or the like from diffusing from the substrate 100 into thesemiconductor layer 103 and for increasing the adhesive performance of afilm formed on the substrate 100. A single layer or a multi-layer of aninorganic insulating film such as a silicon oxide film, a siliconnitride film, a silicon oxy-nitride film or the like can be used as theunderlayer film 101.

For example, the underlayer film 101 can be formed not only by CVD or bysputtering, but also, in the case of using a heat-resistant substratesuch as a quartz substrate, by forming an amorphous silicon film and bythermally oxidizing the amorphous silicon film, to form a silicon oxidefilm.

It is recommended that the material of the semiconductor layer 103 beselected in accordance with a characteristic required of the TFT, andthe following materials can be used as the semiconductor layer 103:amorphous silicon, amorphous silicon germanium, or amorphous germanium,or crystalline silicon, crystalline germanium, or crystalline silicongermanium, each of which is made by crystallizing each of theseamorphous semiconductor films by applying a laser to it or by subjectingit to heating treatment. The thickness of the semiconductor layer 103 ismade 10 nm to 150 nm.

As the insulating film 104 may be used a single-layer or multi-layerfilm of an inorganic insulating film comprising silicon oxide, siliconnitride, or silicon oxy-nitride formed by CVD or sputtering. Forexample, double layered film comprising silicon oxy-nitride film andsilicon oxide film, or triple layered film in which silicon nitride filmis sandwiched by silicon oxide films.

A conductive film 105 forming a gate electrode/wiring is formed on theinsulating film 104. As the conductive film 105, a metal containing Ta,Mo, Ti, Al, and Cu as a major component or an alloy of these metals (forexample, a Ta—Mo alloy, a Ta—Al alloy, or a nitride of tantalum or thelike), or conductive silicon (Si) containing phosphorus or arsenic orsilicide is used.

Next, a photoresist is applied over the conductive film 105 and thesurface of the substrate is exposed to light via a photo-lithographymask and is developed to form a photoresist pattern 106. The conductivefilm 105 is etched by using the photoresist pattern 106 as an etchingmask to form a pattern 107 made of the conductive film (see FIG. 1(C)).

After the photoresist pattern 106 is removed, impurities to be donors(to be specific, phosphorus or arsenic) or impurities to be an acceptors(to be specific, boron) are added to the semiconductor layer 103 underconditions of an acceleration voltage of 10 KV to 80 KV, a dose of1×10¹⁴/cm² to 1×10¹⁷/cm². Here, phosphorus ions are added by ion doping.The pattern 107 functions as a doping mask and N-type impurity regions108, 109 are formed in the semiconductor layer 103 in a self-alignmentmanner. In order to add the impurities, ion implantation, ion diffusionor the like can be used in addition to ion doping (see FIG. 1(D)).

A positive-working photoresist is applied to the whole surface of thesubstrate such that it covers the pattern 107 made of the conductivefilm. In this state, the photoresist is exposed to light applied to theback of the substrate, and then is developed to forma photoresistpattern 110 (see FIG. 2(A)).

When the photoresist is exposed to the light applied from the back ofthe substrate, the pattern 107 made of the conductive film functions asa mask obstructing the light applied to the back of the substrate andhence a pattern 110 is formed on the pattern 107 which is not exposed tothe light. In the present invention, by elongating an exposing time (byover-exposing), a photoresist pattern 110 narrower than the pattern 107can be formed. Here, lengths ΔL1, ΔL2 by which the photoresist pattern110 is narrowed in the direction of length of a channel, compared withthe pattern 107, are controlled by an exposing time and a developingtime. Also, the lengths of the low-concentration impurity regions aredetermined by the lengths ΔL1, ΔL2.

Next, the pattern 107 made of the conductive film is etched by using thephotoresist pattern 110 as the etching mask to form a gate electrode 111narrower in the direction of length of a channel than the pattern 107(see FIG. 2(B)).

The photoresist pattern 110 is removed and then the insulating film 104is etched by using gate electrode 111 as the etching mask to form a gateinsulating film 112 in a self-alignment manner, whereby the side of thegate insulating film 112 is aligned with the side of the gate electrode111 to make the same plane. In this connection, in the case where theetching selectivity of the semiconductor layer 103 can not be made largein this etching process, it is preferable to omit the etching process ofthe insulating film 104.

By using the gate electrode 111 as a doping mask, the same impurities(here, phosphorus) as these added to the impurity regions 108, 109 areadded to the semiconductor layer 103 at an acceleration voltage of 10 KVto 80 KV and a dose of 1×10¹²/cm² to 1×10¹⁵/cm², whereby N⁺-type sourceregion 115 and drain region 116 and N⁻-type low-concentration impurityregions 117, 118, and a channel forming region 119 are formed in aself-alignment manner. It is recommended that the concentration ofphosphorus in the source region 115 and the drain region 116 be 1×10¹⁹atoms/cm³ to 1×10²¹ atoms/cm³ and that the concentration of phosphorusin the low-concentration impurity regions 117, 118 be 1×10¹⁶ atoms/cm³to 1×10¹⁹ atoms/cm³ (see FIG. 2(D)).

In the present invention, since the light is applied to the back of thesubstrate so as to form the photoresist pattern 110, the width of thephotoresist pattern 110 can be determined by the exposing time and thedeveloping time, and hence the width can be controlled by the exposingtime and the developing time with higher accuracy than by alignment. Asa result, the length and the position of the low-concentration impurityregions 117, 118 can be controlled with high accuracy. Further, sinceone photo-lithography mask is not required, cost is reduced andthroughput is improved.

The impurities added to the semiconductor layer 103 are activated bysubjecting them to heat treatment and/or by exposing them to a laser.Then, they are subjected to heat treatment in a hydrogen atmosphere toterminate the dangling bonds in the semiconductor layer 103 by thehydrogen. After the hydrogenating process is finished, a silicon oxidefilm or the like is formed as an interlayer insulating film 120. Theinterlayer insulating film 120 is patterned to make contact holes forthe source region 115, the drain region 116, and a gate wiring. Aconductive film made of titanium, aluminum, or the like is formed andpatterned to form a source electrode 121, a drain electrode 122, and alead electrode (not shown) of the gate wiring.

Preferred Embodiment 2

In the preferred embodiment 1, a method of manufacturing a TFT having anLDD structure has been described, and in this preferred embodiment, amethod of manufacturing a TFT having an offset structure will bedescribed. The present preferred embodiment will be described by usingFIGS. 1 and 2.

In the case of the present preferred embodiment, the impurity addingprocess shown in FIG. 2(D) is omitted, and in the impurity addingprocess shown in FIG. 1(D), a high concentration doping is performed ata dose of 1×10¹⁵/cm² to 1×10¹⁷/cm² so that the concentration ofphosphorus becomes 1×10¹⁹ atoms/cm³ to 1×10²¹ atoms/cm³, therebysufficiently reducing sheet resistance. As a result, a TFT can bemanufactured in which the regions 117, 118 become offset regions.

EXAMPLES

The examples in accordance with the present invention will hereinafterbe described in detail with reference to FIGS. 3 to 8.

Example 1

The present example is the one applied to a CMOS circuit. Themanufacturing process of the CMOS circuit of the present example will bedescribed with reference to FIG. 3 and FIG. 4. FIGS. 3 and 4 arecross-sectional views along the direction of length of the channel ofthe TFT.

A glass substrate 200 is prepared. In the present example, a 1737 glasssubstrate made by Corning Glass Corp. is used. An underlayer film 201 isformed on the surface of the glass substrate 200. A silicon oxide filmhaving a thickness of 200 nm is formed by plasma CVD by using TEOS(tetra ethoxy silane) gas as a raw material. The underlayer film 201 isheated at 400° C. for 4 hours.

An amorphous silicon film having a thickness of 500 nm is formed on theunderlayer film 201 by plasma enhanced CVD (hereinafter referred to asPECVD) by the use of SiH₄ diluted with an H₂ gas. A low pressure CVD maybe used instead of the PECVD. The amorphous silicon film is heated anddehydrogenated at 450° C. for one hour, whereby the content of hydrogenatom in the amorphous silicon film is made not more than 5%, and morepreferably, not more than 1%. The dehydrogenated amorphous silicon isirradiated with excimer laser light to form a crystalline(polycrystalline) silicon film 203.

The conditions of crystallization by a laser are as follows: XeClexcimer laser is used as a laser light source; Laser light is formed byan optical system in linear light; And an overlap ratio is 96% and alaser energy density is 359 mJ/cm² (see FIG. 3(A)).

In addition to the PECVD, a low pressure CVD or sputtering may be usedas a method of forming the amorphous silicon film. Also, in order tocrystallize the amorphous silicon film, a laser of a continuousexcitation type like an Ar laser may be used other than a laser of anoscillation type like an excimer laser. Further, in order to crystallizethe amorphous silicon film, a lamp annealing using a halogen lamp or amercury lamp, or a heating at a temperature 600° C. or more may beperformed instead of applying a laser.

Next, a photoresist pattern (not shown) is formed by a photo-lithographyprocess and then the crystalline silicon film 203 is patterned by theuse of the photoresist pattern to form active layers 205, 206. Aninsulating film 207 to be a gate insulating film is formed such that itcovers the active layers 205, 206. Here, a silicon oxy-nitride filmhaving a thickness of 120 nm is formed by PECVD by using SiH₄ and NO₂ asraw material gases. Then, a conductive laminated film is formed whichcomprises an N-type silicon film 208 containing phosphorus and atantalum film 209. Each film is formed by sputtering and the siliconfilm 208 is 200 nm thick and the tantalum film is 150 thick (see FIG.3(B)).

The photoresist is exposed to light via a photo-lithography mask and isdeveloped to form a photoresist pattern 210. The tantalum film 209 andthe silicon film 208 are patterned by using the photoresist pattern 210as the etching mask to form a pattern 211 to be a prototype of a gatewiring. These films are etched by a dry etching process using a O₂ gasand a CF₄ gas. A reference numeral 211 a designates an N-type siliconlayer and a reference numeral 211 b designates a tantalum layer. In thepresent embodiment, the gate wiring of an N-channel type TFT isintegrally formed with the gate wiring of a P-channel type TFT.

The photoresist pattern 210 is removed, and then a photoresist pattern213 is formed which covers the active layer 205 of the P-channel typeTFT. Phosphorus ions are added to the semiconductor layer 206 by iondoping. The ion doping is performed by using phosphine diluted withhydrogen as a doping gas at an acceleration voltage of 80 KV and a doseof 1×10¹⁵/cm². The pattern 211 functions as a doping mask to form N-typeimpurity regions 215, 216 in the semiconductor film 206 in aself-alignment manner.

The photoresist pattern 213 is removed, and then a new photoresistpattern 217 is formed. In this case, a positive photoresist is appliedso that it covers the pattern 211 and is exposed to the light appliedfrom the back of the substrate and is developed to form the photoresistpattern 217 on the pattern 211. In the present example, the photoresistpattern 217 is made narrower than the pattern 211 by controlling anexposing time (see FIG. 4(A)).

The pattern 211 is etched by using the photoresist pattern 217 as theetching mask to form a gate wiring 218. In the gate wiring 218, partscrossing the semiconductor layers 205, 206 are gate electrodes. In thegate wiring 218, a reference numeral 218 a designates an N-type siliconlayer and a reference numeral 218 b designates a tantalum layer (seeFIG. 4(B)).

The photoresist pattern 217 is removed, and then an insulating film 207is patterned by using the gate wiring 218 as the etching mask to form agate insulating film 219. A photoresist pattern 220 is formed whichcovers the active layer 206 of the N-channel type TFT. The photoresistpattern 220 is formed by applying light to the surface of the substratevia a photo-lithography mask.

Phosphorus ions are added to the semiconductor layer 206 by ion doping.The ion doping is performed by using phosphine diluted with hydrogen asa doping gas at an acceleration voltage of 10 KV and a dose of3×10¹³/cm². The gate wiring (gate electrode) 218 functions as a dopingmask and N⁺-type source region 221 and drain region 222, N -typelow-concentration impurity regions 223 and 224, and channel formingregion 225 are formed in the semiconductor film 206 in a self-alignmentmanner.

A photoresist pattern 230 covering the N-channel type TFT is formed.Boron ions are added to the active layer 205 by ion doping. The dopingis performed by using diboron diluted with hydrogen as a doping gas atan acceleration voltage of 10 KV and a dose of 2×10¹⁵/cm². The gatewiring (gate electrode) 218 functions as a doping mask and P⁺-typesource region 231 and drain region 232 and a channel forming region 233are formed in a self-alignment manner (see FIG. 4(D)).

In the present example, three photoresist patterns 213, 220, 230 areformed so that phosphorus is not added to the semiconductor layer 206 ofthe P-channel type TFT, but it is also possible to omit two photoresistpatterns 213, 220 which are used for doping the phosphorus, whichresults in simplifying the manufacturing process and in improvingthroughput. In this regard, by forming the photoresist patterns 213, 220like the present example, the sheet resistance of the N-type and P-typeimpurity regions formed in the semiconductor layer can be controlledwith higher accuracy.

In the case of omitting the photoresist patterns 213, 220, thephosphorus is added to the semiconductor layer 205 of the P-channel typeTFT and the N-type impurity region is formed, and hence in the boronadding process shown in FIG. 4(D), it is necessary to determine a doseso that the conductive type of the N-type impurity region is reversedinto P-type.

The photoresist pattern 230 is removed, and then the active layers 205,206 are irradiated with laser light and then are subjected to heattreatment to activate the phosphorus and boron added. The laser lightirradiation is performed at a pulse frequency of 50 Hz, a laser energydensity of 179 mJ/cm² and a substrate temperature of 150° C., and theheat treatment is performed in a nitrogen atmosphere at 450° C. for 2hours. Next, the substrate is heated in a 100% hydrogen atmosphere at350° C. for 1 hour to terminate dangling bonds of the semiconductorlayer by hydrogen.

Next, as the interlayer insulating film 240, a laminated film comprisinga silicon nitride having a thickness of 20 nm and a silicon oxide filmhaving a thickness of 900 nm is formed by the PECVD method. Contactholes, that lead to the source regions 221, 231 and the drain regions222, 232, and a contact hole reaching the terminal part of the gatewiring 218 are formed in the interlayer insulating film 240. A laminatedfilm comprising titanium (150 nm)/aluminum (500 nm)/titanium (100 nm) isformed on the interlayer insulating film 240 by sputtering and ispatterned to form source wirings 241, 242, a drain wiring 243, and thelead wiring (not shown) of the gate wiring 218, whereby a CMOS circuitis manufactured on the glass substrate.

In this regard, in the present example, the N-channel type TFT has anLDD structure, but it may easily be manufactured in an offset structureas described.

Example 2

The present preferred example is the one in which the CMOS circuitmanufacturing process described in the example 1 is applied to themanufacturing process of the active matrix substrate of the liquidcrystal panel.

FIG. 5 is a schematic constitution of the active matrix type liquidcrystal panel. The liquid crystal panel has a structure in which theliquid crystal is sandwiched by an active matrix substrate and anopposite substrate thereof. The active matrix substrate is the one inwhich a pixel matrix circuit 501 using a TFT as the switching element ofa pixel electrode is formed on the glass substrate 500.

Further, the TFT is manufactured by using the crystalline silicon in thepresent example, and hence a gate wiring driving circuit 502 and asource wiring driving circuit 503 for driving the pixel matrix circuit501 are also formed on the glass substrate 500. Still further, externalterminals for applying electric power or a control signal to the drivingcircuits 502, 503 are formed on the glass substrate 500 and a FPC 505 isconnected to the external terminals.

The gate wiring driving circuit 502 and the source wiring drivingcircuit 503 are mainly constituted by CMOS circuits, and are connectedto the pixel matrix circuit 501 by gate wirings 430 and source wirings440.

In the pixel matrix circuit 501, the gate wiring is formed for everycolumn and the source wiring 440 is formed for every row. A pixel TFT400 is formed near the crossing part of the gate wiring 430 and thesource wiring 440. The gate electrode of the pixel TFT 400 is connectedto the gate wiring 430 and the source thereof is connected to the sourcewiring 440. Further, a pixel electrode 460 and a holding capacity 470 isconnected to the drain thereof.

A transparent conductive film such as an ITO film or the like is formedon the whole surface of an opposite substrate 510 made of glass. Atransparent conductive film is the opposite electrode to the pixelelectrode 460 of the pixel matrix circuit 501 and a liquid material isdriven by an electric field formed between the pixel electrode and theopposite electrode. Further, if necessary, an alignment film and a colorfilter are formed on the opposite substrate 510.

FIG. 6(A) is a top plan view of the pixel matrix circuit 501 and the topplan view of nearly one pixel. FIG. 6(B) is a top plan view of a CMOScircuit constituting the driving circuits 502, 503. FIG. 7 is across-sectional view of the active matrix substrate, and across-sectional view of the pixel matrix circuit 501 and the CMOScircuit. The cross-sectional view of the CMOS circuit corresponds to across-section along a chain line I-I′ in FIG. 6(A), and thecross-sectional view of the pixel matrix circuit 501 corresponds to across-section along a chain line II-II′ in FIG. 6(B).

The CMOS circuit and the pixel TFT of the driving circuit aremanufactured on the glass substrate 500 at the same time. In the CMOScircuit, the active layers 300, 310, a gate insulating film 320, a gatewiring 330 of the first layer are laminated over an interlayer film 510.The gate wiring 330 is constituted by a laminated film comprising anN-type silicon layer 331 and a tantalum layer 332.

In the active layer of the N-channel type TFT, one channel formingregion 301, and a source region 302 and a drain region 303 of theN⁺-type high concentration impurity region are formed. A pair of N⁻-typelow-concentration impurity regions 304 and 305 are formed, one betweenthe channel forming region 301 and the source region 302 and the otherbetween the channel forming region 301 and the drain region 303, incontact with each region. The concentration of the donor (phosphorus orarsenic) of the N⁻-type low concentration impurity regions 304, 305 islower than that of the source region 302 and the drain region 303.

In the active layer of the P-channel type TFT, one channel formingregion 311 and P⁺-type high-concentration impurity regions 312, 313 incontact with the channel forming region 311 are formed. The region 312is a source region and the region 313 is a drain region.

In the pixel matrix circuit 501, an active layer 410, a gate insulatinglayer 420, a gate wiring 430 of the first layer wiring are laminated insequence on the underlayer film 510. The gate wiring 430 is integrallyformed with the gate electrode 430E of the pixel TFT 400, and the gatewiring 430 is formed by a laminated film comprising an N-type siliconlayer 431 and a tantalum layer 432.

In the active layer 410, two channel forming regions 411, 412 areformed. N⁺-type high-concentration impurity regions 413, 414 and 415 areformed such that two of them sandwich the channel forming regions 411,or 412. The regions 413, 414 are a source region and a drain region,respectively. Further, in the active layer, a pair of N⁻-typelow-concentration impurity regions 416, 417 are formed sandwiching thechannel forming region 411 and a pair of N⁻-type low-concentrationimpurity regions 418, 419 are formed sandwiching the channel formingregion 412. The concentration of the donor (phosphorus or arsenic) islower in the low-concentration impurity regions 416, 417, 418, 419 thanin the high-concentration impurity regions 413, 414, 415.

An interlayer insulating film 511 covering the active layers 300, 310,410 is formed on the whole surface of the substrate 500. Sourceelectrodes 341, 342, a drain electrode 343, a source wiring 440, and adrain electrode 441 are formed as the second layer wiring/electrode onthe interlayer insulating film 511. As shown in FIG. 6(A), the drainelectrode 343 is connected to the gate wiring 335 of the other CMOScircuit.

It is recommended that these CMOS circuit and pixel TFT 400 bemanufactured according to the manufacturing process of the example 1.After the TFT is manufactured, as shown in FIG. 7, a first planarizingfilm 512 is formed on the whole surface of the substrate 500. Here,acrylic is applied by spin coating and then is calcined to form anacrylic film having a thickness of 1 μm.

Contact holes are made in the first planarizing film 512. Then, atitanium film having a thickness of 200 nm is formed by sputtering andthen is patterned to form source wirings 351, 352, and a black mask 450.

Next, an acrylic film having a thickness of 0.5 μm is formed as aplanarizing film 513 as is the case with the first planarizing film 512.A contact hole to the drain electrode 441 is made in the planarizingfilm 512, 513. An ITO film is formed by sputtering and then is patternedto form a pixel electrode 460 connected to the drain electrode 441. Theplanarizing film 513 is made a dielectric body at the portion where thepixel electrode 460 overlaps the black mask 450, whereby a holdingcapacity 470 having the pixel electrode 460 and the black mask 450 as apair of electrodes is formed.

In this connection, a reflection type liquid crystal panel can bemanufactured by forming the pixel electrode 460 of a material reflectinga visible spectrum such as aluminum, silver, or the like.

Also, although the active matrix substrate is applied to the liquidcrystal panel in the present example, it is also possible to apply theactive matrix substrate to the other active matrix type display devicesuch as an organic EL or the like. Also, it is easy for a person skilledin this art to manufacture a CMOS-type image sensor by connecting aphotoelectric conversion layer having a PIN junction to the pixel TFT.

Example 3

The active matrix type liquid crystal panel shown in the example 2 canbe utilized as the display device of various kinds of electronic units.The electronic unit described in the present example is defined as aproduct mounted with an active matrix type display device.

As such an electronic unit may be mentioned there are, for example, adisplay device for a computer, a projector, a projection type TV, ahead-mounted display, a video camera, a digital still camera, a carnavigation system, a notebook-type personal computer, a portabletelephone, an electronic notebook, and the like. Examples of theseelectronic units are shown in FIG. 8.

FIG. 8(A) shows a portable telephone comprising a main body 2001, avoice output part 2002, a voice input part 2003, a display device 2004,an operation switch 2005, and an antenna 2006. The present invention canbe applied to the display device 2004 provided with an active matrixsubstrate.

FIG. 8(B) shows a video camera comprising a main body 2101, a displaydevice 2102, a voice input part 2103, an operation switch 2104, abattery 2105, and an image receiving part 2106. The present inventioncan be applied to the display device 2102 having the active matrixsubstrate and the image receiving part 2106.

FIG. 8(C) shows a mobile computer comprising a main body 2201, a camerapart 2202, an image receiving part 2203, an operation switch 2204, and adisplay device 2205. The present invention can be applied to the imagereceiving part 2203 and the display device 2205.

FIG. 8(D) shows a head mounted display comprising a main body 2301, adisplay device 2302, and an arm part 2303 for mounting it on the head.The present invention can be applied to the display device 2302.Further, a microphone or an earphone may be mounted on the head-mounteddisplay as a voice input output device.

FIG. 8(E) shows a rear type projector comprising a main body 2401, alight source 2402, a display device 2403, a polarized beam splitter2404, reflectors 2405, 2406, and a screen 2407. The present inventioncan be applied to the display device 2403.

FIG. 8(F) shows a portable book comprising a main body 2501, a displaydevices 2502, 2503, a memory media 2504, and a scanning switch 2505, andfor displaying data memorized in a mini-disc (MD) or a DVD or datareceived by an antenna. The present invention can be applied to thedisplay device 2503.

As described above, the present invention has an extremely wide range ofapplication and can be applied to the whole category of electronicunits, and in addition to them, also to an electrically illuminatedbulletin board, an advertisement display or the like.

Example 4

This example explains, by referring to FIG. 10, an example case in whichthis invention is applied to a display (organic EL display) using anactive matrix type organic electroluminescence (organic EL) material.FIG. 10(A) shows a circuit diagram of an active matrix type organic ELdisplay having a display area formed on a glass substrate and drivingcircuits formed along the periphery of the display area. The organic ELdisplay comprises a display area 11 formed on the substrate, anX-direction peripheral driving circuit 12, and a Y-direction peripheraldriving circuit 13. The display area 11 comprises a switching TFT 30, astorage capacitance 32, a current control TFT 31, an organic EL element33, X-direction signal lines 18 a, 18 b, power lines 19 a, 19 b, andY-direction signal lines 20 a, 20 b, 20 c.

FIG. 10(B) shows a top view of almost one pixel. The switching TFT 30and the current control TFT 31 are formed in the same way as in then-channel TFT shown in FIG. 3(C) of example 1.

FIG. 11 is a cross section taken along the line of FIG. 10(B), showingthe cross section of the switching TFT 30, storage capacitance 32,current control TFT 31 and organic EL element portion. Over a substrate40, base films 41, 42, gate insulating film 45, first interlayerinsulating film 46, gate electrodes 47, 48, capacitance line 49, sourceand drain lines 18 a, 19 a, 51, 52, and second interlayer insulatingfilm 50 are formed in the same way as in the example 1. Then, over theselayers is formed a third interlayer insulating film 53 in a way similarto the second interlayer insulating film 50. A contact hole reaching thedrain line 52 is formed, after which a pixel electrode 54 made of atransparent conductive film is formed. The organic EL element portioncomprises the pixel electrode 54; an organic EL layer 55 overlying thepixel electrode and the third interlayer insulating film 53; and a firstelectrode 56 made of Mg—Ag compound and a second electrode 57 made ofAl, formed over the organic EL layer 55. If a color filter, though notshown, is used, a color display is possible. By applying the activematrix substrate manufacturing method shown in the examples 1 to 10, theactive matrix type organic EL display can be fabricated easily.

TFT of the active matrix type organic EL display shown in this examplecan be manufactured according to the method of the example 1. The TFTconstitution of this example can suitably be applied to an organic ELdisplay described above.

Example 5

This example demonstrates another process for producing an EL(electroluminescence) display device according to the invention of thepresent application.

FIG. 12A is a top view showing an EL display device, which was producedaccording to the invention of the present application. In FIG. 12A,there are shown a substrate 4010, a pixel part 4011, a driving circuitfrom the source 4012, and a driving circuit from the gate 4013, eachdriving circuit connecting to wirings 4014-4016 which reach FPC 4017leading to external equipment.

The pixel part, preferably together with the driving circuit, isenclosed by a covering material 6000, a sealing material (or housingmaterial) 7000, and an end-sealing material (or second sealing material)7001.

FIG. 12B is a sectional view showing the structure of the EL displaydevice in this Example. There is shown a substrate 4010, an underlyingcoating 4021, a TFT 4022 for the driving circuit, and a TFT 4023 for thepixel unit. (The TFT 4022 shown is a CMOS circuit consisting of ann-channel type TFT and a p-channel type TFT. The TFT 4023 shown is theone, which controls current to the EL element.) These TFTs may be of anyknown structure (top gate structure or bottom gate structure).

Incidentally, the present invention is used in the TFT 4022 for thedriving circuit and the TFT 4023 for the pixel unit.

Upon completion of TFT 4022 (for the driving circuit) and TFT 4023 (forthe pixel unit), with their active layer being the semiconductor layerformed according to the invention of the present application, a pixelelectrode 4027 is formed on the interlayer insulating film (planarizingfilm) 4026 made of a resin. This pixel electrode is a transparentconductive film, which is electrically connected to the drain of TFT4023 for the pixel unit. The transparent conductive film may be formedfrom a compound (called ITO) of indium oxide and tin oxide or a compoundof indium oxide and zinc oxide. On the pixel electrode 4027 is formed aninsulating film 4028, in which is formed an opening above the pixelelectrode 4027.

Subsequently, the EL layer 4029 is formed. It may be of single-layerstructure or multi-layer structure by freely combining known ELmaterials such as injection layer, hole transport layer, light emittinglayer, electron transport layer, and electron injection layer. Any knowntechnology may be available for such structure. The EL material iseither a low-molecular material or a high-molecular material (polymer).The former may be applied by vapor deposition, and the latter may beapplied by a simple method such as spin coating, printing, or ink-jetmethod.

In this example, the EL layer is formed by vapor deposition through ashadow mask. The resulting EL layer permits each pixel to emit lightdiffering in wavelength (red, green, and blue). This realizes the colordisplay. Alternative systems available include the combination of colorconversion layer (CCM) and color filter and the combination of whitelight emitting layer and color filter. Needless to say, the EL displaydevice may be monochromatic.

On the EL layer is formed a cathode 4030. Prior to this step, it isdesirable to clear moisture and oxygen as much as possible from theinterface between the EL layer 4029 and the cathode 4030. This objectmay be achieved by forming the EL layer 4029 and the cathode 4030consecutively in a vacuum, or by forming the EL layer 4029 in an inertatmosphere and then forming the cathode 4030 in the same atmospherewithout admitting air into it. In this Example, the desired film wasformed by using a film-forming apparatus of multi-chamber system(cluster tool system).

The multi-layer structure composed of lithium fluoride film and aluminumfilm is used in this Example as the cathode 4030. To be concrete, the ELlayer 4029 is coated by vapor deposition with a lithium fluoride film (1nm thick) and an aluminum film (300 nm thick) sequentially. Needless tosay, the cathode 4030 may be formed from MgAg electrode which is a knowncathode material. Subsequently, the cathode 4030 is connected to awiring 4016 in the region indicated by 4031. The wiring 4016 to supply aprescribed voltage to the cathode 4030 is connected to the FPC 4017through an electrically conductive paste material 4032.

The electrical connection between the cathode 4030 and the wiring 4016in the region 4031 needs contact holes in the interlayer insulating film4026 and the insulating film 4028. These contact holes may be formedwhen the interlayer insulating film 4026 undergoes etching to form thecontact hole for the pixel electrode or when the insulating film 4028undergoes etching to form the opening before the EL layer is formed.When the insulating film 4028 undergoes etching, the interlayerinsulating film 4026 may be etched simultaneously. Contact holes of goodshape may be formed if the interlayer insulating film 4026 and theinsulating film 4028 are made of the same material.

Then, a passivation film 6003, a filling material 6004 and a coveringmaterial 6000 are formed so that these layers cover the EL element.

Furthermore, the sealing material 7000 is formed inside of the coveringmaterial 6000 and the substrate 4010 such as surrounding the EL element,and the end-sealing material 7001 is formed outside of the sealingmaterial 7000.

The filling material 6004 is formed to cover the EL element and alsofunctions as an adhesive to adhere to the covering material 6000. As thefilling material 6004, PVC (polyvinyl chloride), an epoxy resin, asilicon resin, PVB (polyvinyl butyral), or EVA (ethylenvinyl acetate)can be utilized. It is preferable to form a desiccant in the fillingmaterial 6004, since a moisture absorption can be maintained.

Also, spacers can be contained in the filling material 6004. It ispreferable to use spherical spacers comprising barium oxide to maintainthe moisture absorption in the spacers.

In the case of that the spaces are contained in the filling material,the passivation film 6003 can relieve the pressure of the spacers. Ofcourse, the other film different from the passivation film, such as anorganic resin, can be used for relieving the pressure of the spacers.

As the covering material 6000, a glass plate, an aluminum plate, astainless plate, a FRP (Fiberglass-Reinforced Plastics) plate, a PVF(polyvinyl fluoride) film, a Mylar film, a polyester film or an acrylfilm can be used. In a case that PVB or EVA is employed as the fillingmaterial 6004, it is preferable to use an aluminum foil with a thicknessof some tens of μm sandwiched by a PVF film or a Mylar film.

It is noted that the covering material 6000 should have a lighttransparency with accordance to a light emitting direction (a lightradiation direction) from the EL element.

The wiring 4016 is electrically connected to FPC 4017 through the gapbetween the sealing material 7000 and the end-sealing material 7001, andthe substrate 4010. As in the wiring 4016 explained above, other wirings4014 and 4015 are also electrically connected to FPC 4017 under thesealing material 4018.

Example 6

In this example, another EL display device having a different structurefrom the example 5 is explained, as shown in FIGS. 13A and 13B. The samereference numerals in FIGS. 13A and 13B as in FIGS. 12A and 12B indicatesame constitutive elements, so an explanation is omitted.

FIG. 13A shows a top view of the EL module in this example and FIG. 13Bshows a sectional view of V-V′ of FIG. 13A.

According to Example 5, the passivation film 6003 is formed to cover asurface of the EL element.

The filling material 6004 is formed to cover the EL element and alsofunctions as an adhesive to adhere to the covering material 6000. As thefilling material 6004, PVC (polyvinyl chloride), an epoxy resin, asilicon resin, PVB (polyvinyl butyral), or EVA (ethylenvinyl acetate)can be utilized. It is preferable to form a desiccant in the fillingmaterial 6004, since a moisture absorption can be maintained.

Also, spacers can be contained in the filling material 6004. It ispreferable to use spherical spacers comprising barium oxide to maintainthe moisture absorption in the spacers.

In the case of that the spaces are contained in the filling material,the passivation film 6003 can relieve the pressure of the spacers. Ofcourse, the other film different from the passivation film, such as anorganic resin, can be used for relieving the pressure of the spacers.

As the covering material 6000, a glass plate, an aluminum plate, astainless plate, a FRP (Fiberglass-Reinforced Plastics) plate, a PVF(polyvinyl fluoride) film, a Mylar film, a polyester film or an acrylfilm can be used. In a case that PVB or EVA is employed as the fillingmaterial 6004, it is preferable to use an aluminum foil with a thicknessof some tens of μm sandwiched by a PVF film or a Mylar film.

It is noted that the covering material 6000 should have a lighttransparency with accordance to a light emitting direction (a lightradiation direction) from the EL element.

Next, the covering material 6000 is adhered using the filling material3404. Then, the flame material 6001 is attached to cover side portions(exposed faces) of the filling material 6004. The flame material 6001 isadhered by the sealing material (acts as an adhesive) 6002. As thesealing material 6002, a light curable resin is preferable. Also, athermal curable resin can be employed if a heat resistance of the ELlayer is admitted. It is preferable for the sealing material 6002 not topass moisture and oxygen. In addition, it is possible to add a desiccantinside the sealing material 6002.

The wiring 4016 is electrically connected to FPC 4017 through the gapbetween the sealing material 6002 and the substrate 4010. As in thewiring 4016 explained above, other wirings 4014 and 4015 are alsoelectrically connected to FPC 4017 under the sealing material 6002.

Example 7

In this example, the structure of the pixel region in the panel isillustrated in more detail. FIG. 14 shows the cross section of the pixelregion; FIG. 15A shows the top view thereof; and FIG. 15B shows thecircuit pattern for the pixel region. In FIG. 14, FIG. 15A and FIG. 15B,the same reference numerals are referred to for the same parts, as beingcommon thereto.

In FIG. 14, the switching TFT 3502 formed on the substrate 3501 is NTFTof the invention (cf. Examples 1 to 3). In this Example, it has adouble-gate structure, but its structure and fabrication process do notso much differ from the structures and the fabrication processesillustrated hereinabove, and their description is omitted herein.However, the double-gate structure of the switching TFT 3502 hassubstantially two TFTs as connected in series, and therefore has theadvantage of reducing the off-current to pass therethrough. In thisExample, the switching TFT 3502 has such a double-gate structure, but isnot limitative. It may have a single-gate structure or a triple-gatestructure, or even any other multi-gate structure having more than threegates. As the case may be, the switching TFT 3502 may be PTFT of theinvention.

The current-control TFT 3503 is NTFT of the invention. The drain wire3535 in the switching TFT 3502 is electrically connected with the gateelectrode 3537 in the current-control TFT, via the wire 3536therebetween. The wire indicated by 3538 is a gate wire for electricallyconnecting the gate electrodes 3539 a and 3539 b in the switching TET3502.

It is very important that the current-control TFT 3503 has the structuredefined in the invention. The current-control TFT is a unit forcontrolling the quantity of current that passes through the EL device.Therefore, a large quantity of current passes through it, and the unit,current-control TFT has a high risk of thermal degradation anddegradation with hot carriers. To this unit, therefore, the structure ofthe invention is extremely favorable, in which an LDD region is soconstructed that the gate electrode overlaps with the drain area in thecurrent-control TFT, via a gate-insulating film therebetween.

In this Example, the current-control TFT 3503 is illustrated to have asingle-gate structure, but it may have a multi-gate structure withplural TFTs connected in series. In addition, plural TFTs may beconnected in parallel so that the channel-forming region issubstantially divided into plural sections. In the structure of thattype, heat radiation can be effected efficiently. The structure isadvantageous for protecting the device with it from thermaldeterioration.

As in FIG. 15A, the wire to be the gate electrode 3537 in thecurrent-control TFT 3503 overlaps with the drain wire 3540 therein inthe region indicated by 3504, via an insulating film therebetween. Inthis state, the region indicated by 3504 forms a capacitor. Thecapacitor 3504 functions to retain the voltage applied to the gate inthe current-control TFT 3503. The drain wire 3540 is connected with thecurrent supply line (power line) 3501, from which a constant voltage isall the time applied to the drain wire 3540.

On the switching TFT 3502 and the current-control TFT 3503, formed is afirst passivation film 3541. On the film 3541, formed is a planarizingfilm 3542 of an insulating resin. It is extremely important that thedifference in level of the layered parts in TFT is removed throughplanarization with the planarizing film 3542. This is because the ELlayer to be formed on the previously formed layers in the later step isextremely thin, and if there exist a difference in level of thepreviously formed layers, the EL device will be often troubled by lightemission failure. Accordingly, it is desirable to previously planarizeas much as possible the previously formed layers before the formation ofthe pixel electrode thereon so that the EL layer could be formed on theplanarized surface.

The reference numeral 3543 indicates a pixel electrode (a cathode in theEL device) of an electroconductive film with high reflectivity. Thepixel electrode 3543 is electrically connected with the drain in thecurrent-control TFT 3503. It is preferable that the pixel electrode 3543is of a low-resistance electroconductive film of an aluminum alloy, acopper alloy or a silver alloy, or of a laminate of those films.Needless-to-say, the pixel electrode 3543 may have a laminate structurewith any other electroconductive films.

In the recess (this corresponds to the pixel) formed between the banks3544 a and 3544 b of an insulating film (preferably of a resin), thelight-emitting layer 44 is formed. In the illustrated structure, onlyone pixel is shown, but plural light-emitting layers could be separatelyformed in different pixels, corresponding to different colors of R(red), G (green) and B (blue). The organic EL material for thelight-emitting layer may be any π-conjugated polymer material. Typicalpolymer materials usable herein include polyparaphenylenevinylene (PVV)materials, polyvinylcarbazole (PVK) materials, polyfluorene materials,etc.

Various types of PVV-type organic EL materials are known, such as thosedisclosed in “H. Shenk, H. Becker, O. Gelsen, E. Klunge, W. Kreuder, andH. Spreitzer; Polymers for Light Emitting Diodes, Euro DisplayProceedings, 1999, pp. 33-37” and in Japanese Patent Laid-Open No.92576/1998. Any of such known materials are usable herein.

Concretely, cyanopolyphenylenevinylenes may be used for red-emittinglayers; polyphenylenevinylenes may be for green-emitting layers; andpolyphenylenevinylenes or polyalkylphenylenes may be for blue-emittinglayers. The thickness of the film for the light-emitting layers may fallbetween 30 and 150 nm (preferably between 40 and 100 nm).

These compounds mentioned above are referred to merely for examples oforganic EL materials employable herein and are not limitative at all.The light-emitting layer maybe combined with a charge transportationlayer or a charge injection layer in any desired manner to form theintended EL layer (this is for light emission and for carrier transferfor light emission).

Specifically, this Example is to demonstrate the example of usingpolymer materials to form light-emitting layers, which, however, is notlimitative. Apart from this, low-molecular organic EL materials may alsobe used for light-emitting layers. For charge transportation layers andcharge injection layers, further employable are inorganic materials suchas silicon carbide, etc. Various organic EL materials and inorganicmaterials for those layers are known, any of which are usable herein.

In this Example, a hole injection layer 46 of PEDOT (polythiophene) orPAni (polyaniline) is formed on the light-emitting layer 3545 to give alaminate structure for the EL layer. On the hole injection layer 46,formed is an anode 3547 of a transparent electroconductive film. In thisExample, the light having been emitted by the light-emitting layer 3545radiates therefrom in the direction toward the top surface (that is, inthe upward direction of TFT). Therefore, in this, the anode musttransmit light. For the transparent electroconductive film for theanode, usable are compounds of indium oxide and tin oxide, and compoundsof indium oxide and zinc oxide. However, since the anode is formed afterthe light-emitting layer and the hole injection layer having poor heatresistance have been formed, it is preferable that the transparentelectroconductive film for the anode is of a material capable of beingformed into a film at as low as possible temperatures.

When the anode 3547 is formed, the EL device 3505 is finished. The ELdevice 3505 thus fabricated herein indicates a capacitor comprising thepixel electrode (cathode) 3543, the light-emitting layer 3545, the holeinjection layer 4 and the anode 3547. As in FIG. 15A, the region of thepixel electrode 43 is nearly the same as the area of the pixel.Therefore, in this, the entire pixel functions as the EL device.Accordingly, the light utility efficiency of the EL device fabricatedherein is high, and the device can display bright images.

In this Example, a second passivation film 3548 is formed on the anode3547. For the second passivation film 3548, preferably used is a siliconnitride film or a silicon oxynitride film. The object of the film 3548is to insulate the EL device from the outward environment. The film 48has the function of preventing the organic EL material from beingdegraded through oxidation and has the function of preventing it fromdegassing. With the second passivation film 3548 of that type, thereliability of the EL display device is improved.

As described hereinabove, the EL display panel of the inventionfabricated in this Example has a pixel region for the pixel having theconstitution as in FIG. 14, and has the switching TFT through which theoff-current to pass is very small to a satisfactory degree, and thecurrent-control TFT resistant to hot carrier injection. Accordingly, theEL display panel fabricated herein has high reliability and can displaygood images.

The constitution of this Example can be combined with any constitutionof Examples 1 to 2 in any desired manner. Incorporating the EL displaypanel of this Example into the electronic appliance of Example 3 as itsdisplay part is advantageous.

Example 8

This Example is to demonstrate a modification of the EL display panel ofExample 7, in which the EL device 3505 in the pixel region has areversed structure. For this Example, referred to is FIG. 16. Theconstitution of the EL display panel of this Example differs from thatillustrated in FIG. 15A only in the EL device part and thecurrent-control TFT part. Therefore, the description of the other partsexcept those different parts is omitted herein.

In FIG. 16, the current-control TFT 3701 may be PTFT of the invention.For the process of forming it, referred to is that of Example 1 and 2.

In this Example, the pixel electrode (anode) 3550 is of a transparentelectroconductive film. Concretely, used is an electroconductive film ofa compound of indium oxide and zinc oxide. Needless-to-say, also usableis an electroconductive film of a compound of indium oxide and tinoxide.

After the banks 51 a and 51 b of an insulating film have been formed, alight-emitting layer 3552 of polyvinylcarbazole is formed between themin a solution coating method. On the light-emitting layer 3552, formedare an electron injection layer 3553 of acetylacetonatopotassium(hereinafter acacK), and a cathode 3554 of an aluminum alloy. In thiscase, the cathode 3554 serves also as a passivation film. Thus isfabricated the EL device 3701.

In this Example, the light having been emitted by the light-emittinglayer radiates in the direction toward the substrate with TFT formedthereon, as in the direction of the arrow illustrated.

The constitution of this Example can be combined with any constitutionof Examples 1 and 2 in any desired manner. Incorporating the EL displaypanel of this Example into the electronic appliance of Example 3 as itsdisplay part is advantageous.

Example 9

This Example is to demonstrate modifications of the pixel with thecircuit pattern of FIG. 15B. The modifications are as in FIG. 17A toFIG. 17C. In this Example illustrated in those FIG. 17A through FIG.17C, 3801 indicates the source wire for the switching TFT 3802; 3803indicates the gate wire for the switching TFT 3802; 3804 indicates acurrent-control TFT; 3805 indicates a capacitor; 3806 and 3808 indicatecurrent supply lines; and 3807 indicates an EL device.

In the example of FIG. 17A, the current supply line 3806 is common tothe two pixels. Specifically, this example is characterized in that twopixels are lineal-symmetrically formed with the current supply line 3806being the center between them. Since the number of current supply linescan be reduced therein, this example is advantageous in that the pixelpattern can be much finer and thinner.

In the example of FIG. 17B, the current supply line 3808 is formed inparallel to the gate wire 3803. Specifically, in this, the currentsupply line 3808 is so constructed that it does not overlap with thegate wire 3803, but is not limitative. Being different from theillustrated case, the two may overlap with each other via an insulatingfilm therebetween so far as they are of different layers. Since thecurrent supply line 3808 and the gate wire 3803 may enjoy the commonexclusive area therein, this example is advantageous in that the pixelpattern can be much finer and thinner.

The structure of the example of FIG. 17C is characterized in that thecurrent supply line 3808 is formed in parallel to the gate wires 3803,like in FIG. 38B, and that two pixels are lineal-symmetrically formedwith the current supply line 3808 being the center between them. Inthis, it is also effective to provide the current supply line 3808 insuch a manner that it overlaps with any one of the gate wires 3803.Since the number of current supply lines can be reduced therein, thisexample is advantageous in that the pixel pattern can be much finer andthinner.

The constitution of this Example can be combined with any constitutionof Example 1 through 6 in any desired manner. Incorporating the ELdisplay panel having the pixel structure of this Example into theelectronic appliance of Example 3 as its display part is advantageous.

Example 10

The figure of Example 7, that are illustrated in FIG. 15A and FIG. 15Bis provided with the capacitor 3504 which acts to retain the voltageapplied to the gate in the current-control TFT 3503. In the example,however, the capacitor 3504 may be omitted.

In the Example 7, the current-control TFT 3503 is NTFT of the invention,as shown in Examples 1 and 2. Therefore, in the example, the LDD regionis so formed that it overlaps the gate electrode with thegate-insulating film interposed therebetween. In the overlapped region,a parasitic capacitance is formed, as generally referred to as a gatecapacitance. The present example is characterized in that the parasiticcapacitance is positively utilized in place of the capacitor 3504.

The parasitic capacitance in question varies, depending on the area inwhich the gate electrode overlaps with the LDD region, and is thereforedetermined according to the length of the LDD region in the overlappedarea.

Also as illustrated in FIG. 17A, FIG. 17B and FIG. 17C of Example 9, thecapacitor 3805 can be omitted.

The constitution of this Example can be combined with any constitutionof Examples 1 through 6 in any desired manner. Incorporating the ELdisplay panel having the pixel structure of the present example into theelectronic appliance of Example 19 as its display part is advantageous.

According to the present invention, a photoresist pattern determiningthe length of a low-concentration impurity region can be formed in aself-alignment manner by exposing a substrate to the light applied tothe back of the substrate, and hence the length of the low-concentrationimpurity region can be controlled with higher accuracy in the presentinvention than in the conventional embodiment shown in FIG. 9. Also,since the present invention does not need an anodic oxidation process,it can facilitate the integration of a circuit and does not limit thematerial of a gate wiring to aluminum.

1-11. (canceled)
 12. An active matrix type display device comprising: asubstrate; a pixel part on the substrate; a pixel matrix circuit in thepixel part, the pixel matrix circuit comprising pixels forming a matrixof pixels, each pixel comprising: a first wire and a second wire eachalong a first direction; a third wire along a second directionintersecting the first direction; a first transistor comprising a gateelectrode, a first terminal and a second terminal, the first terminalbeing electrically connected to the first wire; a second transistorcomprising a gate electrode, a first terminal and a second terminal, thegate electrode being electrically connected to the second terminal ofthe first transistor and the first terminal being electrically connectedto the second wire and the third wire; and a capacitor comprising afirst terminal and a second terminal, the first terminal beingelectrically connected to the gate electrode of the second transistor;and a covering material, a sealing material and an end-sealing materialenclosing the pixel part, wherein each of the sealing material and theend-sealing material are interposed between the substrate and thecovering material, and wherein the end-sealing material covers a sideedge portion of the covering material.
 13. An active matrix type displaydevice comprising: a substrate; a pixel part on the substrate; a pixelmatrix circuit in the pixel part, the pixel matrix circuit comprisingpixels forming a matrix of pixels, each pixel comprising: a first wireand a second wire each along a first direction; a third wire along asecond direction intersecting the first direction; a first transistorcomprising a gate electrode, a first terminal and a second terminal, thefirst terminal being electrically connected to the first wire; a secondtransistor comprising a gate electrode, a first terminal and a secondterminal, the gate electrode being electrically connected to the secondterminal of the first transistor and the first terminal beingelectrically connected to the second wire and the third wire; acapacitor comprising a first terminal and a second terminal, the firstterminal being electrically connected to the gate electrode of thesecond transistor; and an EL element electrically connected to thesecond terminal of the second transistor; and a covering material, asealing material and an end-sealing material enclosing the pixel part,wherein each of the sealing material and the end-sealing material areinterposed between the substrate and the covering material, wherein theend-sealing material covers a side edge portion of the coveringmaterial, and wherein the second transistor is configured to control aquantity of current passing through the EL element.
 14. An active matrixtype display device comprising: a substrate; a pixel part on thesubstrate; a pixel matrix circuit in the pixel part, the pixel matrixcircuit comprising pixels forming a matrix of pixels, each pixelcomprising: a first wire and a second wire each along a first direction;a third wire along a second direction intersecting the first direction;a first transistor comprising a gate electrode, a first terminal and asecond terminal, the first terminal being electrically connected to thefirst wire; a second transistor comprising a gate electrode, a firstterminal and a second terminal, the gate electrode being electricallyconnected to the second terminal of the first transistor and the firstterminal being electrically connected to the second wire and the thirdwire; and a capacitor comprising a first terminal and a second terminal,the first terminal being electrically connected to the gate electrode ofthe second transistor; and a covering material, a sealing material andan end-sealing material enclosing the pixel part, wherein each of thesealing material and the end-sealing material are interposed between thesubstrate and the covering material, wherein the end-sealing materialcovers a side edge portion of the covering material, and wherein thefirst terminal and the second terminal of the capacitor are respectivelyformed from a same layer as the gate electrode of the second transistorand from a same layer as the first terminal of the second transistor.15. The active matrix type display device according to claim 12, whereinthe second terminal of the capacitor is electrically connected to thesecond wire and the third wire.
 16. The active matrix type displaydevice according to claim 13, wherein the second terminal of thecapacitor is electrically connected to the second wire and the thirdwire.
 17. The active matrix type display device according to claim 14,wherein the second terminal of the capacitor is electrically connectedto the second wire and the third wire.
 18. The active matrix typedisplay device according to claim 12, wherein each of the second wireand the third wire are formed from a same conductive layer.
 19. Theactive matrix type display device according to claim 13, wherein each ofthe second wire and the third wire are formed from a same conductivelayer.
 20. The active matrix type display device according to claim 14,wherein each of the second wire and the third wire are formed from asame conductive layer.
 21. The active matrix type display deviceaccording to claim 12, wherein each of the first terminal of the firsttransistor, the second wire and the third wire are formed from a sameconductive layer.
 22. The active matrix type display device according toclaim 13, wherein each of the first terminal of the first transistor,the second wire and the third wire are formed from a same conductivelayer.
 23. The active matrix type display device according to claim 14,wherein each of the first terminal of the first transistor, the secondwire and the third wire are formed from a same conductive layer.
 24. Anelectronic device comprising the active matrix type display deviceaccording to claim
 12. 25. An electronic device comprising the activematrix type display device according to claim
 13. 26. An electronicdevice comprising the active matrix type display device according toclaim 14.